//
// TimedNotificationQueue.h
//
// Library: Foundation
// Package: Notifications
// Module:  TimedNotificationQueue
//
// Definition of the TimedNotificationQueue class.
//
// Copyright (c) 2009, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_TimedNotificationQueue_INCLUDED
#define Foundation_TimedNotificationQueue_INCLUDED


#include <map>
#include "Poco/Clock.h"
#include "Poco/Event.h"
#include "Poco/Foundation.h"
#include "Poco/Mutex.h"
#include "Poco/Notification.h"
#include "Poco/Timestamp.h"


namespace Poco
{


class Foundation_API TimedNotificationQueue
/// A TimedNotificationQueue object provides a way to implement timed, asynchronous
/// notifications. This is especially useful for sending notifications
/// from one thread to another, for example from a background thread to
/// the main (user interface) thread.
///
/// The TimedNotificationQueue is quite similar to the NotificationQueue class.
/// The only difference to NotificationQueue is that each Notification is tagged
/// with a Timestamp. When inserting a Notification into the queue, the
/// Notification is inserted according to the given Timestamp, with
/// lower Timestamp values being inserted before higher ones.
///
/// Notifications are dequeued in order of their timestamps.
///
/// TimedNotificationQueue has some restrictions regarding multithreaded use.
/// While multiple threads may enqueue notifications, only one thread at a
/// time may dequeue notifications from the queue.
///
/// If two threads try to dequeue a notification simultaneously, the results
/// are undefined.
{
public:
    TimedNotificationQueue();
    /// Creates the TimedNotificationQueue.

    ~TimedNotificationQueue();
    /// Destroys the TimedNotificationQueue.

    void enqueueNotification(Notification::Ptr pNotification, Timestamp timestamp);
    /// Enqueues the given notification by adding it to
    /// the queue according to the given timestamp.
    /// Lower timestamp values are inserted before higher ones.
    /// The queue takes ownership of the notification, thus
    /// a call like
    ///     notificationQueue.enqueueNotification(new MyNotification, someTime);
    /// does not result in a memory leak.
    ///
    /// The Timestamp is converted to an equivalent Clock value.

    void enqueueNotification(Notification::Ptr pNotification, Clock clock);
    /// Enqueues the given notification by adding it to
    /// the queue according to the given clock value.
    /// Lower clock values are inserted before higher ones.
    /// The queue takes ownership of the notification, thus
    /// a call like
    ///     notificationQueue.enqueueNotification(new MyNotification, someTime);
    /// does not result in a memory leak.

    Notification * dequeueNotification();
    /// Dequeues the next pending notification with a timestamp
    /// less than or equal to the current time.
    /// Returns 0 (null) if no notification is available.
    /// The caller gains ownership of the notification and
    /// is expected to release it when done with it.
    ///
    /// It is highly recommended that the result is immediately
    /// assigned to a Notification::Ptr, to avoid potential
    /// memory management issues.

    Notification * waitDequeueNotification();
    /// Dequeues the next pending notification.
    /// If no notification is available, waits for a notification
    /// to be enqueued.
    /// The caller gains ownership of the notification and
    /// is expected to release it when done with it.
    ///
    /// It is highly recommended that the result is immediately
    /// assigned to a Notification::Ptr, to avoid potential
    /// memory management issues.

    Notification * waitDequeueNotification(long milliseconds);
    /// Dequeues the next pending notification.
    /// If no notification is available, waits for a notification
    /// to be enqueued up to the specified time.
    /// Returns 0 (null) if no notification is available.
    /// The caller gains ownership of the notification and
    /// is expected to release it when done with it.
    ///
    /// It is highly recommended that the result is immediately
    /// assigned to a Notification::Ptr, to avoid potential
    /// memory management issues.

    bool empty() const;
    /// Returns true iff the queue is empty.

    int size() const;
    /// Returns the number of notifications in the queue.

    void clear();
    /// Removes all notifications from the queue.
    ///
    /// Calling clear() while another thread executes one of
    /// the dequeue member functions will result in undefined
    /// behavior.

protected:
    typedef std::multimap<Clock, Notification::Ptr> NfQueue;
    Notification::Ptr dequeueOne(NfQueue::iterator & it);
    bool wait(Clock::ClockDiff interval);

private:
    NfQueue _nfQueue;
    Event _nfAvailable;
    mutable FastMutex _mutex;
};


} // namespace Poco


#endif // Foundation_TimedNotificationQueue_INCLUDED
